1. Field of Invention
The present invention relates to a hydro-metallurgical process for producing metals by means of leaching a mineral, particularly a production process of base and precious metals from copper ore or copper-ore concentrates. More particularly, the present invention relates to a metal-winning method for effectively hydraulically leaching the copper ore or copper-ore concentrates, followed by electrolysis of the leached liquor using a diaphragm-type cell.
2. Description of Related Art
Most copper ores which are subjected to smelting are sulfide ores. Among them, chalcopyrite is the most frequently smelted. Meanwhile, the sulfide minerals may also be subjected to a hydrometallurgical process, which is roughly classified into an atmospheric pressure leaching method and a pressurized leaching method. Known atmospheric pressure leaching methods are an acid-leaching method and a halide-leaching method. The halide leaching method known in U.S. Pat. No. 5,487,819 (hereinafter simply referred to as the U.S. Patent) is a national U.S. phase application of PCT/AU93/00311 (WO94/00606).
The US Patent proposes leaching in a halide bath. This method is referred to as the INTEC method. One or more minerals are transferred from a high-oxidation potential zone to a low-oxidation potential zone during the halide leaching in an acidic pH region. The fundamental steps of the US Patent are illustrated in FIG. 1. The treatment of the respective steps is described in the US Patent as follows.
(1) Liquor is fed from the low-oxidation potential zone to an electrolytic cell and is rendered to high-oxidation potential by electrolysis. This liquor is transferred to the high-oxidation potential zone and is brought into contact with the mineral(s) so as to leach at least partly the metals of the mineral(s). The leached metals are transferred to the low-oxidation potential zone to convert the atomic valence of the leached metals to a low oxidation valence.
(2) The electrolyte is transferred from the low-oxidation potential zone to the electrolytic step. In this step, the electrolysis is performed to form at least one metal and to enhance the oxidation potential of the electrolyte. As a result, the electrolyte leaving the electrolytic step has higher oxidation potential than that transferred to the electrolytic step.
(3) The electrolyte, the oxidation-potential of which has been increased, is returned to the high oxidation-potential zone of the leaching step.
The U.S. Patent emphasizes such advantages as high productivity due to high cathode current-density, and the capability to leach such metals as gold. In the U.S. Patent, the diaphragm-electrolysis is carried out in such a manner that current is conducted through the diaphragm consisting of glass fiber and the like and surrounding an anode. The leach liquor is, for example, copper-chloride solution. The oxidizing agent, which creates the high oxidation-reduction potential in the solution having high Cl concentration, is Cu2+, Br2, BrCl2− and the like. The chalcopyrite mineral can be totally leached, for example, by Cu2+ as the oxidizing agent (Reactions (1) through (4)). The metallic compounds including gold, which remains in the leaching residue, can be totally leached by Br2 and BrCl2− (Reaction (18)). When copper is recovered from the liquor in step (2) mentioned above, Cu2+ is reduced in the cathode compartment of the diaphragm-electrolytic cell. Simultaneously, Cu2+ is formed in the anode compartment by the ionic oxidation of Cu, and Br2 and BrCl2− are formed by Cl− and Br−. In step (3), Br2 and BrCl2− are returned to the leaching step of the high oxidation potential zone (14R, FIG. 1).
The liquor fed into the cathode compartment as electrolyte has high Cu concentration (FIG. 1, reference numeral 33; FIG. 2, reference numeral 52), which is then decreased in step (2). Subsequently, the electrolyte is passed through the diaphragm and is transferred to the anode compartment (FIG. 1, 70). The anolyte is present in the anode compartment, where Cu2+, Br2 and BrCl2− are formed due to the electrolytic oxidation. The resultant catholyte is then withdrawn as described hereinabove. The liquor moves through the diaphragm by utilizing the pressure difference between the liquors separated by the diaphragm. The withdrawn liquor has oxidation-reduction potential (ORP) exceeding 600 mV (vs Ag/AgCl, the ORP mentioned below is also in terms of Ag/AgCl) and is hence so oxidative that all metals including gold can be leached from the copper-leached residue.
An oxidation reaction in the anode compartment proceeds by Equation 16, i.e., Br−+2Cl−→BrCl2−+2e. The resultant Br2 and BrCl2− are used as the oxidizing agent in the leaching step.
Recovery of Ag+ consists of two main steps. Namely, one of the steps is subjecting the leach liquor to Cu cementation so as to attain approximately 20 mg/L of the Ag+ concentration. The other step is electrolyzing in the Ag recovery apparatus until from 1 to 2 mg/L of Ag+ concentration is attained.